I've been making an OBD-II data logger with Arduino, which logs data like vehicle speed, engine RPM etc., to a SD card. With my OBD-II adapter for Arduino, this is not difficult implement. I used a small OLED display module to display status and some realtime data of the vehicle.

Currently it looks like this:

Logged data is rendered with HighCharts like following. Actually I am going to make the rendering a web service so everyone can view the data easily.

I have published my sketch and some more details on here on my website. The source code of this OBD-II data logger uses following Arduino libraries:

Hi, I'm just getting started and woud like to know how much engine data is available via OBD-II, I tried following the link to your website but no luck

Regards Richard

Pretty much all of it. The biggest dependency is your vehicle and whether or not it reports a specific piece of data, but you can assume all the basics (RPM, MPH, temp, etc.) will be available, and of course any time your "check engine" light comes on there's an OBD code associated with that as well.